Here’s where things get really interesting. The SU16D9 is the shortest and lightest of the SU16 line. The main difference between it and the SU16C are the 9″ barrel and compact forend. But they come at a price, because the SU16D9 is an NFA item and unfortunately tax stamps are still a thing. If you’re looking for an extremely light, compact and capable 5.56 short-barreled rifle, the D9 is for you.